Major League Baseball postseason in the context of "League Championship Series"

Major League Baseball (MLB) is a professional baseball league in North America composed of 30 teams, divided equally between the National League (NL) and the American League (AL), with 29 in the United States and 1 in Canada. MLB is one of the major professional sports leagues in the United States and Canada and is considered the premier professional baseball league in the world. Each team plays 162 games per season, with Opening Day held during the last week of March or the first week of April. Six teams in each league then advance to a four-round postseason tournament in October, culminating in the World Series, a best-of-seven championship series between the two league champions first played in 1903. MLB is headquartered in Midtown Manhattan.

Formed in 1876 and 1901, respectively, the NL and AL cemented their cooperation with the National Agreement in 1903, making MLB the oldest major professional sports league in the United States and Canada. They remained legally separate entities until 2000, when they merged into a single organization led by the commissioner of baseball. Baseball's first all-professional team, the Cincinnati Red Stockings, was founded in 1869. The first few decades of professional baseball saw rivalries between leagues, and players often jumped from one team or league to another. These practices were essentially ended by the National Agreement of 1903, in which AL and NL agreed to respect each other's player contracts, including the contentious reserve clause, which bound players to their teams.

The World Series is the annual championship series of Major League Baseball (MLB). It has been contested since 1903 between the champion teams of the American League (AL) and the National League (NL). The winning team, determined through a best-of-seven playoff (except in 1903 and from 1919–1921, when a best-of-nine format was used), is awarded the Commissioner's Trophy.

The series is traditionally played in October, although before expansion of the regular-season schedule from 154 to 162 games the event occasionally started in late September (most recently in 1955) and the entire 1918 series took place early in that month due to the World War I "Work or Fight" order forcing an early end to that year's regular season, while some more recent editions have been contested into November due to in-season delays and expansion of earlier postseason rounds. Because the series is played in the fall (autumn) season in North America, it is often referred to as the Fall Classic.

In Major League Baseball (MLB), the wild card teams are the three teams in each of the two leagues (American and National) that qualify for the postseason despite failing to win their division; the three wild card teams in each league possess the three best winning percentages in their league after the league's three division winners. The wild card was first instituted in MLB in 1994 after the playoff was expanded from 4 teams to 8 teams and MLB divisions were realigned to feature 3 divisions in each league instead of 2, which meant that one non-division winner per league made the playoff and would face a division winner in the first round Division Series.

In 2012, the system was modified to add a second wild card team per league (expanding the playoffs to 10 teams). And the wild card teams played against each other in a play-in game – the MLB Wild Card Game – the winner of which would then advance to the Division Series and play the team with the best record in their league. The two teams with the best records outside of the division champions advanced to the wild card game. The two wild card teams could come out of the same division so there was no guarantee a team that came in second place in their division would make the playoffs.

The Willie Mays World Series Most Valuable Player (MVP) Award is given to the Major League Baseball (MLB) player deemed to have the most impact on his team's performance in the World Series, which is the final round of the MLB postseason. The award was first presented in 1955 by Sport magazine, but since 1985 has been officially presented by MLB. The winner is determined during the final game of the World Series by a committee of reporters and officials present at the game.

On September 29, 2017, the award was renamed in honor of Willie Mays in remembrance of the 63rd anniversary of The Catch, which occurred the year before the award's debut; Mays never won the award himself.